Error detection code generating method and error detection code generator

ABSTRACT

In a mobile communication system, an error detection code or a quality frame indicator (e.g., CRC) is generated using selectively frame information, and at least one of a WCA identifier of another terminal, and a corresponding terminal identifier. And the terminal identifier can be implicitly transmitted to the receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of prior U.S. patent application Ser.No. 12/178,115 filed on Jul. 23, 2008, which is a Divisional Applicationof prior U.S. patent application Ser. No. 10/307,416 filed Dec. 2, 2002(now U.S. Pat. No. 7,546,511), which claims priority under 35 U.S.C.5119 to Korean Application Nos. P2001-76756 and P2001-76757 filed onDec. 5, 2001 and this application is related to U.S. application Ser.No. 10/259,292 filed Sep. 30, 2002, whose entire disclosures areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication system, and moreparticularly, to an error detection code generating method and an errordetection code generator in a mobile communication system.

2. Background of the Related Art

Typically, radio communication systems for transferring packet data usephysical channels, such as, Packet Data Channel (hereinafter referred toas PDCH), Packet Data Control Channel (hereinafter referred to as PDCCH)and so forth.

The PDCH is a channel for use of transferring packet data that actuallyneeds to be transferred to a relevant terminal, mobile station or user(hereinafter being used interchangeably). Many users prefer the PDCHbased on the Time Division Multiplexing system (hereinafter referred toas TDM system). The PDCCH contains control information, enabling aterminal to receive the data being transferred through the PDCH withouterror.

FIG. 1 illustrates a control message format and a number of informationbits transmitted through PDCCH according to a related art for a TDMsystem. The ARQ (automatic request) channel identifier and subpacketidentifier are binary information bits informing the terminal of whetherinformation including PDCH corresponding to PDCCH is to be retransmittedor not. The encoder packet size is binary information bits informing adata information bit number transmitted on PDCH. The MAC identifier is aterminal identifier, and values except (000000)₂ indicate that controlinformation of PDCCH is transferred to which terminal.

When a base station transfers packet data using TDM system, or schedulesdata and later sending the data to each terminal in sequence, the packetdata, which is transmitted to every terminal, always uses all of theavailable resources, e.g., Walsh codes, in the PDCH. Even when only apart of the available resources needs to be used, all of the resourcesare still used for the packet data. As a result thereof, most of otherresources are wasted at the same time.

For example, data sent on PDCH need to be coded and decoded based onWalsh codes. Serial bits are converted to parallel, and the parallelbits are coded using the Walsh codes. In order to decode the data, theinformation regarding the Walsh codes is sent on the PDCCH.

In TDM system, there are plurality of time intervals 1, 2, 3, 4, 5, 6,etc, and only one of a plurality of terminals is allotted for each timeinterval where a PDCH and PDCCH are sent to the terminal during thisallotted time interval. For example, if there are users 1 and 3 and timeintervals 1 and 3, respectively, and if all 32-ary Walsh codes areavailable for use by terminal 1, all 32-ary Walsh codes are utilized inthe PDCH during time interval 1. However, if the available Walsh codesdecrease in time interval 3, all decreased Walsh codes are utilized forthe PDCH. Even before terminal 3 can use the changed/decreased Walshcodes in time interval 3, it needs to know this information. In order toachieve this, the BS broadcasts such information using a Walsh CodeSpace Identification Identifier (WSI) field in the PDCCH (without PDCH)with MAC_ID field information bit of (000000)₂ before time interval 3 toall terminals within a cell. And, the base station explicitly transmitsa control message including MAC_ID to the terminals on PDCCH.

A base station regularly or irregularly broadcasts WSI on the PDCCHwithout the PDCH to all terminals under its management. In the course ofthe broadcast, the base station uses every possible power for allterminals (even including terminals in the worst environment) to be ableto receive the information such that even the terminals in the worstenvironment can receive the WSI. Hence, the broadcasting consumes muchpower. Moreover, when the WSI change, the base station has to inform thechanges to all terminals every time. In those cases, the base stationcannot transmit PDCH, so the transmission efficiency of the entiresystem is consequently reduced.

The above references are incorporated by reference herein whereappropriate for appropriate teachings of additional or alternativedetails, features and/or technical background.

SUMMARY OF THE INVENTION

An object of the invention is to solve at least the above problemsand/or disadvantages and to provide at least the advantages describedhereinafter.

An object of the present invention is to provide a modified controlmessage format.

Another object of the present invention is to provide an additionalfield for the control message format and reduce the number of bits ofthe control message format.

A further object of the invention is to improve the error detectioncapability of the PDCCH.

Another object of the present invention is to provide an error detectioncode generating method and an error detection code generator enabling toincrease a use efficiency of resources and improve an error detectioncapability.

A further another object of the present invention is to transmit anMAC_ID implicitly.

To achieve at least these and other advantages in whole or in part,there is provided in a mobile communication system using time divisionmultiplexing and code division multiplexing, an error detection codegenerating method according to the present invention is characterized inthat an error detection code is generated using selectively a controlinformation for data transmission, a Walsh space indication identifierof another terminal, and a corresponding terminal identifier.

To further achieve at least these and other advantages in whole or inpart, there is provided a method that includes generating a first errordetection code using the control information for the data transmissionand the Walsh space indication identifier of another terminal andgenerating a second error detection code using the first error detectioncode and the terminal identifier.

Preferably, wherein 0 or 1 bits are padded on the terminal identifier sothat a length of the terminal identifier coincides with that of thefirst error detection code.

Preferably, the Walsh space indication identifier of another terminaland terminals identifier are not transmitted to a terminal to which thedata will be transmitted.

Preferably, the step of generating the second error detection codefurther includes a step of carrying out an exclusive or operation on thefirst error detection code and corresponding terminal identifier.

Preferably, the method further includes adding the second errordetection code to the control information for the data transmission.

Preferably, the method includes initializing an error detection codegenerator using the terminal identifier and generating an errordetection code from the initialized error detection code generator usingthe control information for the data transmission.

Preferably, the method includes initializing an error detection codegenerator using the terminal identifier and generating an errordetection code from the initialized error detection code generator usingthe control information for the data transmission and the Walsh spaceindication identifier of another terminal.

Preferably, the method includes initializing an error detection codegenerator using the terminal identifier and Walsh space indicationidentifier of another terminal and generating an error detection codefrom the initialized error detection code generator using the controlinformation for the data transmission.

Preferably, the control information for the data transmission includesan identifier of a retransmission channel used for retransmission, asubpacket identifier in the retransmission channel, a data size of achannel through which the data are transmitted, and a Walsh spaceindication identifier of a corresponding terminal.

To further achieve at least these and other advantages in whole or inpart and in accordance with the purpose of the present invention, asembodied and broadly described herein, there is provided in a mobilecommunication system using time division multiplexing and code divisionmultiplexing, an apparatus for generating an error detection code ischaracterized in that an error detection code is generated usingselectively a control information for data transmission, a Walsh spaceindication identifier of another terminal, and a corresponding terminalidentifier.

Preferably, the apparatus includes an error detection code generatorgenerating a first error detection code using the control informationfor the data transmission and the Walsh space indication identifier ofanother terminal and a modulo operator generating a second errordetection code using the first error detection code and the terminalidentifier.

Preferably, the error detection code generator adds the second errordetection code to the control information for the data transmission soas to transmit.

Preferably, the apparatus is initialized by the terminal identifier andgenerates an error detection code using the control information for thedata transmission.

Preferably, the apparatus is initialized by the terminal identifier andgenerates an error detection code using the control information for thedata transmission and the Walsh space indication identifier of anotherterminal.

Preferably, the apparatus is initialized by the terminal identifier andWalsh space indication identifier of another terminal and generates anerror detection code using the control information for the datatransmission.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objects and advantages of the invention may be realizedand attained as particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

FIG. 1 illustrates a message format of the background art;

FIG. 2 illustrates a message format in accordance with a preferredembodiment;

FIG. 3 illustrates a message format in accordance with a preferredembodiment;

FIG. 4 illustrates a frame structure in accordance with a preferredembodiment;

FIG. 5A illustrates a block diagram of a transmission chain structure ofPDCCH in accordance with a preferred embodiment;

FIG. 5B illustrates a block diagram of a PDCCH transmission structure inaccordance with a preferred embodiment;

FIG. 6A illustrates a block diagram of the outer quality frame qualityindicator of FIG. 5B in accordance with a preferred embodiment;

FIG. 6B illustrates an inner frame quality indicator of FIG. 5B inaccordance with a preferred embodiment;

FIG. 7 illustrates a block diagram of an error detection code additionblock in accordance with a preferred embodiment;

FIG. 8 and FIG. 9 illustrate block diagrams of an error detection codeaddition block in accordance with a preferred embodiment;

FIG. 10 illustrates a diagram of an output result of the error detectioncode addition block shown in FIG. 8 or FIG. 9 in accordance with apreferred embodiment;

FIG. 11 and FIG. 12 illustrate block diagrams of the error detectioncode addition block in accordance with a preferred embodiment;

FIG. 13 illustrates a detailed block diagram of the error detection codeaddition block in accordance with a preferred embodiment; and

FIG. 14 illustrates a diagram of an output result of the error detectioncode addition block shown in FIG. 13 in accordance with a preferredembodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Prior to the description of the present invention, parameters used inthe present invention are explained as follows.

Walsh code is a common name of codes having orthogonality to each otherand used for transmitting physical channels.

Walsh code space is a set of Walsh codes available for the current usewhen a base station transmits packet data, and elements thereof vary inaccordance with time.

PDCH(i) means i^(th) PDCH if at least two PDCHs are available for use.In this case, each of PDCHs divides to use Walsh codes in Walsh codespace.

PDCCH(i), if it is possible for at least two PDCHs to exist, is a commonname of a physical channel including control information that a basestation transmits to terminals in order to receive PDCH(i) successfully.

The present invention related to a packet data transmission system of aTDM/CDM system, whereby a plurality of PDCHs and PDCCHs exist. Hence,expressions of PDCH(i) and PDCCH(i) are used in the followingdescription. In other words, when PDCCH(1), PDCCH(2), . . . , PDCCH(N)and PDCH(1), PDCH(2), . . . , PDCH(N) exists, PDCCH(i) indicates PDCCHthat the base station transmits to the terminal to receive PDCH(i)successfully.

FIG. 2 illustrates the format of the Packet Data Control Channel (PDCCH)Message in accordance with the preferred embodiment (describedhereinafter), over the PDCCH, e.g., forward PDCCH (F-PDCCH). The messageformat of the PDCCH includes an additional field called Walsh CodeAllocation (WCA) field (e.g., CDM Walsh space Identification (CWSI)field/(Last Walsh Code Index (LWSI) field), which preferably preventswasted power consumption caused by broadcasting, and eliminates suchbroadcast. Even if broadcasting is used, the additional field of WCAfield reduces the inefficiencies of a prescribed system. The descriptionof the fields illustrated in FIG. 2 and the various implementation ofthe WCA field can be found in co-pending U.S. application Ser. No.10/259,292 filed Sep. 30, 2002, whose entire disclosure is incorporatedherein by reference.

This message format can be used in both a TDM system, i.e., one PDCHphysical channel and one PDCCH physical channel within a prescribed timeinterval and uses the available Walsh codes, and a Code DivisionMultiplex (CDM) system, i.e., a plurality of PDCH(i) physical channelsand a plurality of PDCCH(i) physical channels, where i is an integernumber that is greater than or equal to 0 , within a prescribed periodof time and the plurality of users are assigned to a plurality ofphysical channels by allocation of the Walsh codes within the Walsh codespace.

In comparing the fields (EP_SIZE, ACID, SPID, MAC_ID, and WCA) of FIG. 1(EP_SIZE, ACID, SPID, and MAC_ID) and FIG. 2 (EP_SIZE, ACID, SPID,MAC_ID, and WCA), the number of information bits has increased from 13bits to 20 bits. With the addition of the WCA field, the number of bitsfor the PDCCH in TDM/CDM mode increased, resulting in more powerconsumption. Hence, there is a need to decrease the number ofinformation bits of the PDCCH fields.

Three following approaches may be used for reducing the number ofinformation bits of the PDCCH:

Method 1 is to use explicit 8 bits MAC_ID and add 8 bits CRC (cyclicredundancy check code), which is a class of linear error detecting codeswhich generate parity check bits by finding the remainder of apolynomial division, for error detection.

Method 2 is to mask the 16 bits CRC with the implicit user MAC_ID andnot to transmit the MAC_ID.

Method 3 is to use a ‘double CRC’, wherein a first CRC is masked by 8bit implicit MAC_ID and a second CRC is added with the first CRC and theMAC_ID is not transmitted.

The advantage of method 1 is that the maximum number of blind decodingsof the forward PDCCH (F-PDCCH) is limited to 4, while method 2 requiresa maximum of 6 blind decodings of F-PDCCH. Therefore, method 1 may be apreferred solution in terms of mobile complexity. The advantage ofmethod 2 is that the UDER (UnDetected Error Ratio) performance is betterthan method 1 due to the increased CRC length.

Method 3 is a hybrid of method 1 and method 2. if two PDCCHs aresupported by a system and the PDCCHs have three types of transmissionformat, Method 3 will provide approximately the same UDER performance asmethod 2, while maintaining the same level of mobile station complexity.Since the complexity of method 1 and method 3 is similar, it isreasonable to choose a method that provides better performance. Hence,the preferred embodiment of the present invention utilizes method 3 forreducing the number of bits of the PDCCH.

In accordance with a preferred embodiment, which uses the third method,FIG. 3 illustrates the message format of PDCCH when the number of bitsof WALSH_MASK, EXT_MSG_TYPE and RESERVED fields equals 0 (see co-pendingU.S. application Ser. No. 10/259,292). As shown therein, the number ofbits of the PDCCH is decreased to 13 bits, even with the additionalsequence number field bits.

The PDCCH frame structure is shown in FIG. 4 including the encoder tailbits of 8 bits. Further, the number of bits can be further reduced bydecreasing the number of bits of the second CRC to be less than 8 bits,e.g., 4 bits, depending upon the system requirements. In order togenerate the PDCCH frame structure, the following steps are used:

Step 1: First CRC bits are calculated based on the 13 input bits of thescrambled PDCCH and masked by the implicit ‘MAC_ID’ and

Step 2: Second CRC bits are calculated based on the 13 input bits andthe first CRC bits generated in step 1.

Step 3: Encoder Tail bits are added.

Depending upon the terminology used, the first CRC may be referred to asthe outer CRC and the second CRC may be referred to as the inner CRC.Alternatively, the first CRC may be referred to as the inner CRC and thesecond CRC may be referred to as the outer CRC depending upon theterminology used. For convenience, the former will be used hereinafterin this preferred embodiment. FIG. 5A illustrates a general blockdiagram of a transmission chain structure of PDCCH in accordance with apreferred embodiment. Referring to FIG. 5A, an input sequence of PDCCH,as shown in FIG. 3, includes an ARQ channel identifier field of 2 bits,an encoder packet size field of 3 bits, and a subpacket identifier fieldof 2 bits, WCA field of 5 bits and optional sequence number field of 1bit. An error detection code such as a CRC (cyclic redundancy checkcode) is added to the input sequence in an error detection code additionblock 101.

Tail bits for sending a final state of a trellis termination are addedto an output sequence of the error detection code addition block 101 ina tail bit addition block 102. The sequence to which the tail bits areadded are encoded as a convolution code in an encoder 103. After theoutputted sequence having been encoded, it is repeated in a symbolrepetition block 104. The repeated bits are punctured in a puncturingblock 105 and thereafter, is interleaved in a block interleaver 106, andthen modulated in a QPSK modulator 107.

FIG. 5B illustrates a detailed PDCCH transmission chain structure inaccordance with a preferred embodiment of the present invention. In thiscase, the base station preferably transmit on the Forward Packet DataControl Channel at prescribed variable data rates, e.g., of 29600,14800, and 7400 bps, depending on the frame duration. The frame durationis preferably NUM_SLOTS (NUM_SLOTS=1, 2, or 4) 1.25-ms slots. All PacketData Control Channels and Packet Data Channels transmittedsimultaneously preferably start their transmissions at the same time(SYS_TIME) and have the same durations.

For a given base station, the I and Q pilot PN sequences for the ForwardPacket Data Control Channel preferably use the same pilot PN sequenceoffset as for the Forward Pilot Channel. The modulation symbolstransmitted on the first Forward Packet Data Control Channel(PDCCH_ID=‘0’) should preferably be transmitted using at least as muchenergy as the modulation symbols transmitted on the second ForwardPacket Data Control Channel (PDCCH_ID=‘1’) that is being transmittedsimultaneously, Nmax_PDCH is 2. See co-pending application Ser. No.10/259,292.

The information transmitted on the Forward Packet Data Control Channelpreferably comprises scrambled SDU[12:0] and the frame qualityindicator-covered SDU[20:13], where SDU (Service Data Unit) is aparameter passed by the MAC Layer. The Forward Packet Data ControlChannel frame preferably comprises scrambled SDU [12:0], the 8-bit framequality indicator-covered SDU[20:13], the 8-bit inner frame qualityindicator (CRC), and the eight Encoder Tail Bits.

First CRC generator 201A and Second CRC generator 201B: The 8-bit framequality indicator-covered SDU[20:13] (first CRC) is generated byperforming the modulo-2 addition of the SDU[20:13] (MAC_ID) passed bythe MAC Layer, with an outer frame quality indicator, which iscalculated on the scrambled SDU[12:0]. Second CRC generator 201B: Theinner frame quality indicator (second CRC) is calculated on all bitswithin the frame, except the inner frame quality indicator itself andthe encoder tail bits.

The tail bit generator (202) generates the last eight bits of eachForward Packet Data Control Channel frame are called the Encoder TailBits. Preferably, each of the eight bits is set to ‘0’. The encoder(203) convolutionally encodes as the PDCCH frame. Preferably, theencoder is initialized to the all-zero state at the end of each frame.The encoded PDCCH frame undergoes code symbol repetition (204) and thecode symbols resulting from the symbol repetition are punctured (205).The modulation symbols on the PDCCH are then interleaved, and theinterleaver block (206) is aligned with the PDCCH frame.

The modulation symbol is provided to the signal point mapping block 207(e.g., modulator) for transmission. FIG. 6A illustrates details of thefirst (outer) CRC generator 201A of FIG. 5. The 8-bit frame qualityindicator-covered SDU[20:13] (first CRC) is generated by performing themodulo-2 addition of the SDU[20:13] (MAC_ID) passed by the MAC Layerwith an outer frame quality indicator, which is calculated on thescrambled SDU[12:0]. The generator polynomial for the outer framequality indicator is based on g(x)=x8+x2+x+1.

Initially, all shift register elements 201 a 0-201 a 7 is preferably setto a logical one and the switches are preferably set in the up position.The register are clocked once for each of the first 13 scrambled inputbits of the Forward Packet Data Control Channel frame with those bits asinput. Then, the switches are set in the down position so that theoutput is a modulo-2 addition with the 8-bit SDU[20:13] and thesuccessive shift register inputs are ‘0’s. Each register is clocked anadditional eight times. These additional bits form the frame qualityindicator-covered SDU[20:13] field, i.e., the outer CRC, which aretransmitted in the order calculated as output.

FIG. 6B illustrates the details of the second (inner) CRC generator 201Billustrated in FIG. 5. The inner frame quality indicator (CRC) isgenerated based on all bits within the frame, except the inner framequality indicator itself and the Encoder Tail Bits. The Forward PacketData Control Channel preferably uses an 8-bit frame quality indicator.The generator polynomial for the inner frame quality indicator ispreferably based on g(x)=x8 +x7+x4+x3+x+1. Herein, the inner framequality indicator and the outer frame quality indicator may be generatedby different polynomials, respectively.

Initially, if the frame duration of the Forward Packet Data ControlChannel is 1.25 or 2.5 ms, all shift register elements 201 b 0-201 b 7are preferably initialized to logical one and the switches arepreferably set in the up position. If the frame duration of the ForwardPacket Data Control Channel is 5 ms, all shift register elements arepreferably initialized to logical zero and the switches are preferablyset in the up position. Each register is clocked once for each of thefirst 21 bits of the Forward Packet Data Control Channel frame withthose bits as input. The switches are set in the down position so thatthe output is a modulo-2 addition with a ‘0’ and the successive shiftregister inputs are ‘0’s. The register is clocked an additional eighttimes. These additional bits shall be the inner frame quality indicatorbits, which are transmitted in the order calculated as output.

FIG. 7 illustrates a block diagram of an error detection code additionblock of FIG. 5A in accordance with another preferred embodiment. InFIG. 7, the error detection code addition block is called aMAC_ID/WCA-CRC generator and an error detection code generated from theMAC_ID/WCA-CRC generator is called a MAC_ID/WCA-CRC code, where WCA ise.g., CWSI or LWCI. The symbol “/” is generally interpreted as “and” or“or.” If “/” is interpreted as an “or,” either the MAC_ID or WCA can beused. If “/” is interpreted as an “and,” both MAC_ID and WCA are used.Referring to FIG. 7, an error detection code added to PDCCH(i) accordingto this preferred embodiment of the present invention, e.g. aMAC_ID/WCA-CRC code, is generated using the input sequence of PDCCH(i)input sequence with WCA(j) and-or MAC identifier (i) (MAC_ID(i)).Selectively, the MAC_ID/WCA-CRC code can be generated using the PDCCH(i)sequence and WCA(j) of another control channel PDCCH(j). In this case,WCA(j) means WCA transmitted on PDCCH(j), where i j and preferably j=i−1when i>1. The MAC identifier(i) is allocated to a terminal or user whichis to receive the information on PDCCH(i).

FIG. 8 illustrates a more detailed block diagram of the error detectioncode addition block illustrated in FIG. 7 in accordance with thispreferred embodiment. A MAC_ID/WCA-CRC generator 201 according to thepresent invention includes a CRC generator 301 generating a general CRCcode and a modulo operator 303.

In this instance, the CRC generator 301 uses PDCCH(i) input sequence(EP_SIZE, ACID, SPID, WCA(i) and AI_SN) of x bits and WCA(j) as inputsso as to generate a CRC code having a general M-bits length. The CRCgenerator 102 is a common name of the CRC generator constituted withtransition registers.

The modulo operator 303 carries out a modulo-2 operation (e.g.,exclusive OR operation) on the general CRC code of M-bits length and anMAC identifier(i) of S-bits length so as to generate a MAC_ID/WCA-CRCcode of M bits. In this case, if S<M, the remaining bits (M-S) arepadded with ‘0’s or ‘1’s in front or rear of the MAC identifier(i) andthe modulo-2 operation is then carried out.

In FIG. 8, WCA(j) and MAC_ID(i) are selectively used to generate theMAC_ID/WCA-CRC code. That is, MAC_ID/WCA-CRC generator uses both oreither of them.

FIG. 9 illustrates a more detailed block diagram of the error detectioncode addition block illustrated in FIG. 7 in accordance with anotherpreferred embodiment. Referring to FIG. 9, a CRC generator 401 includedin a MAC_ID/WCA-CRC generator initializes values of its transitionregisters using the MAC_ID(i). If a length of the MAC identifier(i) isshorter than that for initializing the values of the transitionregisters of the CRC generator 401, ‘0’s or ‘1’s amounting to thenecessary number are padded in front or rear of the MAC identifier(i)and a modulo 2 operation is carried out. The CRC generator 401 havingthe initialized transition registers based on MAC_ID(i) uses an PDCCH(i)input sequence of x-bits number and WCA(j) of PDCCH(j) so as to generatea MAC_ID/WCA-CRC(i) code having an M-bit length. In FIG. 9, WCA(j) andMAC_ID(i) are alternatively used to generate the MAC_ID/WCA-CRC code.That is, MAC_ID/WCA-CRC generator uses both or either of them.

FIG. 10 illustrates a diagram of an output result of each of the errordetection code addition blocks of FIGS. 8 and 9. The MAC_ID/WCA-CRC(i)code is added to the PDDCH(i) input sequence for input to the tail bitaddition block 102 of FIG. 5A. As can be appreciated, the arrangementorder of the MAC_ID/WCA-CRC(i) code and PDCCH(i) input sequence can bereversed. The MAC identifier(i) is used for generating MAC_ID/WCA-CRC(i)and need not be transmitted separately to a receiving end when WCA(j) isnot used (“/”=or). Likewise, when the MAC identifier(i) and WCA(j) areboth used (“/” =and), these parameters need not be transmittedseparately to the receiving end. Instead, the MAC_ID/WCA-CRC(i) andPDCCH(i) input sequence are transmitted to the receiving end.

If only the MAC_ID(i) is used for generating the MAC_ID/WCA-CRC code,(i.e., without WCA(j), there are no special considerations/factor thatneed to be taken into account. However, if the WCA(j) is used with orwithout MAC_ID(j) by the MAC_ID/WCA-CRC generator, the followingoperational factors should be considered.

First Operational Consideration

When N number of PDCH(i)s and N number of PDCCH(i)s are used, a terminalshould recognize MAC identifier(i) and WCA(j) in order to receivePDCCH(i). Hence, in order to receive PDCCH(i), PDCCH(j) needs to becorrectly received in order to interpret WCA(j). If the interpretationof WCA(j) is wrong or incorrect, the terminal is unable to receivePDCCH(i) correctly.

Second Operational Consideration

In the first operational consideration, assuming that j is (i−1), aterminal should recognize MAC identifier(i) and WCA(i-1) in order toreceive the PDCCH(i). In order to receive the PDCCH(i), PDCCH(j-1) needsto be correctly received in order to interpret WCA(i−1). However, avalue of WCA(0) should be determined previously, e.g., WCA (0)=(00000)₂.FIG. 11 illustrates a more detailed block diagram of the error detectioncode addition block of FIG. 7 in accordance with another preferredembodiment. Referring to FIG. 11, a MAC_ID/WCA-CRC generator 201according to the present invention includes a CRC generator 501generating a general CRC code and a modulo operator 502. The CRCgenerator 501 uses PDCCH(i) input sequence of x-bits to generate ageneral CRC code of M-bit length. The modulo operator 502 carries outmodulo operation on the general CRC code and {MAC identifier(i) of Sbits +WCA(j) of Y bits}, where i≠j, so as to generate MAC_ID/WCA-CRC(i)of M bits. If (S+Y)<M, ‘0’s or ‘1’s are padded in front or rear of thesequence comprising the {MAC identifier(i) +WCA(j) }, prior to themodulo 2 operation being carried out. In FIG. 11, WCA(j) and MAC_ID(i)are selectively used to generate the MAC_ID/WCA-CRC code. That is,MAC_ID/WCA-CRC generator uses both or either of them.

FIG. 12 illustrates a more block diagram of the error detection codeaddition block in FIG. 7 in accordance with another preferredembodiment. Referring to FIG. 12, a CRC generator 601 included in aMAC_ID/WCA-CRC generator 201 initializes values of its transitionregisters using {MAC identifier(i) +WCA(j)}, where i≠j. The CRCgenerator 601 having the initialized transition registers uses thePDCCH(i) input sequence of x-bit length as an input so as to generateMAC_ID/WCA-CRC(i) of M-bits length. If a length of the {MACidentifier(i)+WCA(j), i_j} is shorter than that for initializing thevalues of the transition registers of the CRC generator 601, ‘0’s or‘1’s amounting to the necessary number are padded in front or rear ofthe sequence constituted with the {MAC identifier(i)+WCA(j), i≠j} andinitialization is then carried out.

FIG. 13 illustrates a detailed block diagram of the error detection codeaddition block of FIG. 5A in accordance with another preferredembodiment. The error detection code addition block serves as an overlapMAC_ID/WCA-CRC generator 703 to generate an overlap MAC_ID/WCA-CRC code.The overlap MAC_ID/WCA-CRC generator 703 includes a MAC_ID/WCA-CRCgenerator 701 and a CRC generator 702. The CRC generator 702 includestransition registers. The MAC_ID/WCA-CRC generator 701 may comprise anyone of the preferred embodiments shown in FIGS. 8, 9, 11 and 12.

The MAC_ID/WCA-CRC generator 701 uses the PDCCH(i) input sequence ofx-bits, including WCA(j) of Y-bits and a MAC identifier(i) of S-bitsfrom its inputs so as to generate MAC_ID/WCA-CRC(i) of M-bits. The MACidentifier(i) is allocated to a terminal or a user intended to receivethe information on the PDCCH(i).

The CRC generator 702 uses PDCCH(i), and MAC_ID/WCA-CRC(i) sequence togenerate CRC(i) of P bits. The generated CRC(i) and MAC_ID/WCA-CRC(i)are connected to each other to generate the overlap MAC_ID/WCA-CRC(i) ,which is in inputted to a following stage in the transmission chainstructure of FIG. 5A or FIG. 5B.

FIG. 14 illustrates a diagram of an output result of the error detectioncode addition block of FIG. 13. The arrangement order of theMAC_ID/WCA-CRC(i) and PDCCH(i) input sequence can be reversed. Since,the MAC identifier(i) and WCA(j) are used for generatingMAC_ID/WCA-CRC(i), these fields need not be transmitted to a receivingend, and the overlap MAC_ID/WCA-CRC(i) and PDCCH(i) sequence aretransmitted to the receiving end. If the WCA(j) is not used, thisembodiment is quite similar or the same as the embodiment of the doubleCRC.

First Operational Consideration of FIG. 13

When N number of PDCH(i)s and N number of PDCCH(i)s are used, a terminaljudges whether PDDCH(i) is received normally or not through a series ofthe following processes using the overlap MAC_ID/WCA-CRC(i).

The terminal checks CRC(i) in the overlap MAC_ID/WCA-CRC(i) to judgewhether PDDCH(i) is received correctly or not. If a transmission lengthof PDCCH(i) is variable, the terminal recognizes the transmission lengthof PDCCH(i) by checking the CRC(i). Having determined that the PDDCH(i)is correctly received, the terminal judges whether PDCCH(i) is itscontrol channel or not using the MAC_ID/WCA-CRC(i) in the overlapMAC_ID/WCA-CRC(i) as well as judging again as to whether PDCCH(i) iscorrectly received.

In this case, in order to check the MAC_ID/WCA-CRC(i), the terminalneeds to know the MAC identifier(i) independently or both the MACidentifier(i) and WCA(j). In case that the terminal needs to know boththe MAC identifier(i) and WCA(j), PDCCH(j) needs to be correctlyreceived so that WCA(j) can be interpreted in order to receive PDCCH(i).If the interpretation of WCA(j) is wrong, an error will be detected whenMAC_ID/WCA-CRC(i) is checked.

Second Operational Consideration of FIG. 13

If one or more PDCCH(i)'s are simultaneously transmitted, the PDCCH(i)'stransmitted simultaneously have the same transmission length, and aspecific PDCCH(k) and the rest of the PDCCH(i)s (except the specificPDCCH(k)) can have the overlap MAC_ID/WCA-CRC(i)s of differentstructures, respectively.

Assuming that the specific PDCCH(k) is PDCCH(1), the process goes asfollows. The PDDCH(1) generates the overlap MAC_ID/WCA-CRC(1) throughthe same process of FIG. 13, and the terminal checks as to whether anerror of PDDCH(1) has occurred or not through the first operationalconsideration.

The PDCCH(i)s, except PDCCH(1) excludes the generation process of CRC(i)of FIG. 13, and an overlap MAC_ID/WCA-CRC(i) of L bits is generated bythe MAC_ID/WCA-CRC generator. The terminal checks whether errors of thePDCCH(i)s have occurred or not through the first operationalconsideration. Hence, the check for CRC(i) is not carried out.

Third Operational Consideration of FIG. 13

In the first and second operational considerations, assuming that j is(i−1), a terminal should recognize MAC identifier(i) and WCA(i−1) inorder to receive PDCCH(i). In order to receive PDCCH(i), PDCCH(j−1)needs to be correctly received so that WCA(i−1) can be correctlyinterpreted. Hence, a value of WCA(0) needs to be previously determined.For example, it may be that WCA(0) =(00000)₂.

Accordingly, the preferred embodiment enables operation in CDM/TDM mode,thereby reducing waste of available sources. Moreover, the presentinvention uses double CRC or the MAC_ID/WCA-CRC code, thereby reducingthe number of bits of the PDCCH and improving the error detectioncapability of PDCCH(i).

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses. Thedescription of the present invention is intended to be illustrative, andnot to limit the scope of the claims. Many alternatives, modifications,and variations will be apparent to those skilled in the art. In theclaims, means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents but also equivalent structures.

What is claimed is:
 1. A method for transmitting a message over aprescribed channel, the method comprising: generating a first errordetection code based on first information, the first error indicationcode being masked with a terminal identifier; generating a second errordetection code based on the first information and the masked first errorindication code; and transmitting the message over the prescribedchannel, the message comprising the first information, the first errordetection code, and the second error detection code.